In jet weaving machines the weft yarn is inserted through the shed by means of a pulse-like jet of fluid normally air. The necessary jet of pressurized medium is generated by a nozzle device, which in conventional jet weaving machines comprises a nozzle mounted on a sley in the weaving machine which is supplied by a pressure medium from a valve device positioned stationarily in the weaving machine, which is controlled by an electric control unit operating the valve device in synchronism with the operation of the weaving machine. In addition to a so-called main nozzle, which is arranged at the insertion side of the weft yarn in the weaving machine outside the shed, so-called relay-nozzles are arranged on the sley in the shed at equal distances from one another, which relay nozzles are also connected to valve devices which are stationarily arranged in the weaving machine and controlled by the electric control unit thereof. The electric control unit of the weaving machine successively operates the main nozzle and the respective relay nozzles during each pick or weft yarn shot for bringing the weft yarn to the arrival end in the shed. The volume of pressurized medium contained in the ducts between the respective valves and the respective nozzles of these conventional nozzle devices having separate valves and nozzles results in considerable response times which in turn negatively affect the control behaviour of the overall system. Another type of nozzle device having an integrated valve is known from U.S. Pat. No. 4,466,468. This prior art nozzle device comprises a supply for pressurized medium, an outlet nozzle in the form of a passageway through which the weft yarn is guided, a conduit connecting the supply and the outlet nozzle and a valve unit arranged between the supply and the outlet nozzle. The conduit includes an outer storage chamber which, in the open position of the valve unit, is in connection with a cone-shaped duct terminating at the nozzle passageway. The cone-shaped duct and the outer chamber are separated by a rounded edge which is in contact with a flexible diaphragm extending in the radial direction of the device which diaphragm and edge together form the valve unit. The position of the diaphragm is controlled by the pressure of a control air which is fed to the prior art nozzle device by separate solenoids or rotary spool valves. When reducing the pressure of the control air the diaphragm is bent away from the rounded edge so that the pressurized medium flows from the storage chamber to the outlet nozzle. The dynamic control behaviour of this prior art nozzle device is subject to inherent limitations caused by the two-stage valve design necessitating a servo-valve for controlling the operation of the main valve in the form of the diaphragm. In other words, the overall response time of this prior art nozzle device is necessarily longer than the sum of the response times of the servo-valve unit and of the nozzle device itself. Moreover, this prior art nozzle device has a complicated mechanical design caused by the necessity of a diaphragm and a conduit in the form of an outer storage chamber and a cone-shaped duct terminating at the outlet nozzle.
In view of the above prior art nozzle devices, the present invention is based on the object of achieving a nozzle device having a favourable dynamic behaviour although having a relatively simple design.
This object is achieved by a nozzle device in accordance with the claims hereof.
In accordance with the present invention, the valve unit comprises a displaceable soft-magnetic valve body and a coil for generating a magnetic field extending through the soft-magnetic valve body when feeding an actuation current to the coil. The displaceable, soft-magnetic valve body is arranged within the conduit such that the flowing of pressurized medium through the conduit from the supply to the outlet nozzle exerts a force on the valve body having an opposite direction when compared to the direction of the force as generated by the magnetic field. In a preferred embodiment the magnetic field generated by the coil when feeding the actuation current thereto moves the soft-magnetic valve body in its open position allowing a flowing of the pressurized medium from the supply through the conduit to the outlet nozzle. When terminating the actuation current, the pressurized medium flowing along the valve body urges it in its closed position due to frictional forces between the flowing pressurized medium and the valve body itself. When changing the flow direction of the pressurized medium with regard to the direction of movement of the valve body from its open to its closed position, the flowing of pressurized medium can also be used for opening the valve body while closing it due to the magnetic field as generated by the coil when feeding an actuation current thereto.
The valve body preferably has an annular shape, wherein the inner surface of the valve body is in sealing, sliding contact with respect to a cylindric inner wall of the conduit. Although an annular design of the valve body and a cylindric form of the inner wall are preferable for constructional reasons, other cross-sections of the valve body and of the inner wall may also be chosen.
The conduit has an annular portion and surrounds the cylindric, inner wall and the valve body and comprises a radially inwardly extending portion interconnecting the annular portion and the outlet nozzle. Furthermore, the valve body is displaceable in its axial direction for sealing against an essentially radial abutment portion so as to interrupt the radially inwardly extending portion of the conduit. This particular advantage caused by this particular design of the conduit permits a guiding of the pressurized medium along the outer surface of the valve body parallel to its direction of movement in its closed position while it renders possible to manufacture the parts of the nozzle body by machining them.
The valve body has radially extending grooves at its outer surface. These radial grooves increase the friction between the pressurized medium flowing along the outer surface of the valve body and the valve body itself. Hence, the force urging the valve body in its closed position is desirably increased for shortening the closing time of the valve upon terminating the actuation current fed to the coil of the nozzle device.
The valve body has radial bores defining a residual flow of pressurized medium in the closed position of the valve body. The residual flow keeps the resting weft yarn under control.
The valve body preferably consists of an annular portion of soft-magnetic material and a shoe made of elastomeric material. The shoe of elastomeric material forms a sealing surface between the valve body itself and the radial abutment portion.